Silicon steel containing nickel



United States Patent 3,238,073 SILICON STEEL CONTAINING NICKEL Charles Alfred Clark, Birmingham, and John Jefferson Mason, Wednesbury, England, assignors to The International Nickel Company, loo, New York, N.Y., a corporation of Delaware No Drawing. Filed Oct. 31, 1963, Ser. No. 320,534 Claims priority, application Great Britain, Oct. 24, 1963,

3 Claims. (Cl. l483ll.55)

The present invention relates to silicon steels and more particularly to grain-oriented silicon steels which can be given valuable magnetic properties and which are exten sively used as laminations in the cores of transformers and other electrical apparatus.

As is known to those skilled in the art, silicon steels generally have a silicon content between about 3% to about 5%, balance iron. More usually, the silicon is restricted in the range 3.0% to 3.4%. Above this value the steels are not able to be rolled and consequently the steels are unsuitable for use as lamlnations, since grain orientation is produced by the rolling action on the steel. Below 3% silicon the steels have inferior magnetic propcuties. The last step in the manufacture of such steels for use as laminations normally is an annealing step, the thin grain-oriented sheet "being heated in hydrogen or other reducing gas during which the orientation is changed to one in which an easy direction of magnetization is aligned the plane of the strip parallel to .the magnetic field which will be applied to it during the subsequent magnetization step. This annealing step normally is carried out in two stages comprising a short treatment in Wet hydrogen during which the carbon in the steel primarily is removed, and a longer heat treatment in dry hydrogen during which the sulfur in the steel is primarily removed.

The magnetic properties imparted by subsequent magnetization depend in a large part upon the carbon and sulfur contents in the steel as cast, which contents must be finally very low, the carbon content normally not exceeding 0.005% and the sulfur content normally not exceeding 0.005 In the steel as cast, the carbon and sulfur contents are not so low owing to the fact that the final annealing of the thin rolled sheet is, as. stated above, a treatment in which both carbon and sulfur are removed.

It will be appreciated that the composition of the silicon steel changes after the initial grain orientation. However, grain-oriented silicon steel may be defined as steel containing not more than about 0.07% carbon, not more than about 0.04% sulfur and from about 0.05% to about 0.15% manganese. Normally, the balance, except for impurities, is iron but the steels may also contain small amounts of other elements. It is a characteristic of grainoriented silicon steel that it may be magnetized .to have an induction of at least about 17,000 gausses.

It is known that for some purposes the silicon content might advantageous-1y be as high as 6.3% because the electrical resistivity increases and the power losses decrease as the silicon content increase-s. Unfortunately, air melted steels containing more than about 3.5 silicon are so brittle that they cannot satisfactorily be cold rolled. about 4% and still cold roll the steel if the melting is performed under vacuum, but, of course, this increases the expense of manufacture.

It is possible to increase the silicon content to 3,238,073 Patented Mar. 1, 1966 Although attempts have been made to overcome the foregoing difficulties, none as far as we are aware was entirely successful when carried into practice commercially on an industrial scale.

It has now been discovered that the presence of nickel in the silicon steels in question increases their ductility without specifically impairing their magnetic properties and, in particular, without substantially decreasing the resistivity and saturation induction or increasing the magnetostriction or the magnetic anisotropy. It, therefore, becomes possible to increase the silicon content to values giving magnetic properties that are more suitable for some purposes than those of the steels at present on the market and yet which are able to be cold rolled.

it is an object of the present invention to provide grainoriented silicon steels with higher silicon contents but similar ductility to those at present commercially available.

Another object of the invention is to provide grainoriented silicon steels which, while possessing superior ductility to nickel-free steels of similar silicon content, do not have their magnetic properties substantially affected by the presence of nickel.

The invention also contemplates providing structural elements or components for electrical equipment, such as, inter alia, transformer cores, rotors and stators having new and improved combinations of mechanical and magnetic properties.

Generally speaking and in accordance with the invention, an advantageous combination of properties is achieved with silicon steels having a composition from about 3.5% to about 8% silicon and at least about 2% and preferably about 3% nickel. As the silicon increases, the nickel content should valso be increased and at about 7% silicon the nickel content should be at least about 5%. The magnetic properties deteriorate as the nickel content increases over about 6% and, accordingly, it is not desirable to incorporate more nickel in the steel than is required to render it ductile when cold rolled. Thus, with a silicon content of about 4% we prefer to include not more than about 5% nickel in the steel and with a silicon content of about 6%, not more than about 8% nickel. In any case, not more than about 9% nickel is included.

For the purpose of giving those skilled in the :art a better understanding of the invention the following illustrative example is given:

EXAMPLE A cylindrical billet weighing 5 kilograms is forged at 1150 C. to a parallelepiped slab 6" wide, /2" thick. It is then hot rolled to 0.1 inch thick, annealed for 5 minutes at '1000" C. (one hour or more at 700 C.) and the sheet is then cleaned by shot blasting. After this process, the warm rolling is commenced, the metal being immersed in hot water of a temperature of about C. with intermediate annealing as required at 850 C. for half an hour in dry hydrogen. The higher the silicon plus nickel content the more frequently is the need to give the intermediate annealing treatment. In this Way the sheet is brought down to about 0.03 inch thick. The sheet is then annealed and warm rolled without intermediate annealing to 0.014 inch thick. It is this step which introduces optirnum deformation texture in the sheet. The sheet is then 3 heat treated to promote Goss texture and remove the sulfur to a low level.

We believe that the improvement obtained by means of the invention is at least partially the result of grain refinement owing to the presence of nickel.

The fact that the magnetic properties of the silicon steels of the invention are not substantially affected by the presence of nickel is shown in Table I in which the figure given is saturation induction in gausses:

T able] N iekel, Percent Silicon, Percent The improvement in ductility produced by the addition of nickel is shown by the percent elongation figures in Table II. These data were obtained from strip which had been hot rolled and prior to cold roiling, the strip being formed from 4% and 5% silicon steels, respectively. It is at this stage that knowledge concerning the elongation is of value since this is the main criterion for judging the cold rolling properties of the strip at which stage the initial grain orientation is imparted. The 4% silicon steel was tested at room temperature and the 5% silicon steel at 100 C.

Table II Nickel, Percent Silicon. Percent such that the steel can be cold rolled to produce a grainoriented silicon steel of high silicon content whereby a markedly enhanced combination of electrical and magnetic properties is obtained than would otherwise be the case if the steel were not capable of being cold rolled to provide the said grain orientation, said steel consisting of about 3.5% to about 8% silicon and about 3% to 8% nickel with the proviso that the said silicon and nickel are correlated such that as the percentage of silicon is increased above 3.5 the percentage of nickel is increased above 3% such that at about 7% silicon the nickel content is at least 5% and with the further provisos that when the silicon content is about 4% the nickel content does not exceed about 5% and that when the silicon content is about 6% the nickel content does not exceed 8%, carbon in an amount up to not more than 0.07%, up to not more than 0.04% sulfur, about 0.05% and up to not more than about 0.15% manganese, the balance being essentially iron.

2. As a new article of manufacture, a grain-oriented silicon steel formed from the alloy set forth in claim 1, the grain-oriented steel containing carbon in an amount not exceeding about 0.005%.

3. A grain-oriented, ductile, cold workable, h-igh silicon steel characterized not only by good ductility such that the steel can be hot worked but more importantly by a level of ductility such that the steel can be cold rolled to produce a grain-oriented silicon steel of high silicon content whereby a markedly enhanced combination of electrical and magnetic properties is obtained than otherwise would be the case if the steel were not capable of being cold rolled to provide the said grain orientation, said steel consisting of about 3.5 to 8% silicon and from 2% to about 9% nickel with the proviso that the said silicon and nickel are correlated such that as the percentage of silicon is increased above 3.5% the percentage of nickel is increased about 2% such that at about 7% silicon the nickel content is at least 5%, carbon in an amount up to not more than 0.07%, up to not more than 0.04% sulfur, about 0.05 to about 0.15% manganese, the balance being essentially iron,

References (Iited by the Examiner UNITED STATES PATENTS 1,555,234 9/1925 Thuaud l23 1,852,836 4/1932 Corson 75123 2,209,684 7/1940 Crafts 14831.5S

DAVID L. RECK, Primary Examiner, 

1. A DUCTILE, COLD WORKABLE, HIGH SILICON STEEL CHARACTERIZED NOT ONLY BY GOOD DUCTILITY SUCH THAT THE STEEL CAN BE HOT WORKED BUT MORE IMPORTANTLY BY A LEVEL OF DUCTILITY SUCH THAT THE STEEL CAN BE COLD ROLLED TO PRODUCE A GRAINORIENTED SILICON STEEL OF HIGH SILICON CONTENT WHEREBY A MARKEDLY ENCHANCED COMBINATION OF ELECTRICAL AND MAGNETIC PROPERTIES IS OBTAINED THAN WOULD OTHERWISE BE THE CASE IF THE STEEL WERE NOT CAPABLE OF BEING COLD ROLLED TO PROVIDE THE SAID GRAIN ORIENTATION, SAID STEEL CONSISTING OF ABOUT 3.5% TO ABOUT 8% SILICON AND ABOUT 3% TO 8% NICKEL WITH THE PROVISO THAT THE SAID SILICON AND NICKEL ARE CORRELATED SUCH THAT AS THE PERCENTAGE OF SILICON IS INCREASED ABOVE 3.5% THE PERCENTAGE OF NICKEL IS INCREASED ABOVE 3% SUCH THAT AT ABOUT 7% SILICON THE NICKEL CONTENT IS AT LEAST 5% AND WITH THE FURTHER PROVISOS THAT WHEN THE SILICON CONTENT IS ABOUT 4% THE NICKEL CONTENT DOES NOT EXCEED ABOUT 5% AND THAT WHEN THE SILICON CONTENT IS ABOUT 6% THE NICKEL CONTENT DOES NOT EXCEED 8%, CARBON IN AN AMOUNT UP TO NOT MORE THAN 0.07%, UJP TO NOT MORE THAN 0.04% SULFUR, ABOUT 0.05% AND UP TO NOT MORE THAN ABOUT 0.15% MANGANESE, THE BALANCE BEING ESSENTIALLY IRON. 